In the movement of heavy materials, it is common practice to use a crane or hoist whose downwardly-extending cable is provided with a hook, the hook being connected to the load by one or more flexible slings. A sling of this type usually consists of an elongated webbing having a soft eye at each end for engagement with the horn of the hook. The bight of the sling passes under the load and transfers the weight from the load to the hook.
Because the load is often a massive article with sharp edges, such as steel I-beams and the like, the sling can be and frequently is subjected to an abrasive action. When excessive wear takes place, it is usually at the edge of the sling and this can lead to breakage of the sling. Because the material being lifted is not only heavy but also awkward in shape, the possibility of accidental breakage of the supporting sling cannot be tolerated. The appearance of the slightest wear on the sling leads, therefore, to its being discarded, which is an expensive action. In addition, separation or weakening of the sling can take place even before visible wear takes place, because it is sometimes loaded to over its safe working load.
In addition, webbing of the type above described is often used to tie down heavy cargo, where it is desired to secure the cargo against movement. Such tie-down webbing is also subjected to abrasion and cutting at its edges, and hence the same problems that exist with cargo slings also exist with tie-down webbing.
Because wear, i.e., abrasion or cutting, seems to take place most readily on the edges of the webbing, attempts have been made in the past to increase the resistance to wear at that part of the sling. Various methods for increasing the wear and cut resistance of the edges of fabric strips have been developed, as shown in the Johnson U.S. Pat. No. 2,659,958 (Fourdrinier wire having reinforced coated marginal portions), in the Walter U.S. Pat. No. 3,526,565 (treated warp yarn made into sheet, then heated to fuse and form a web), in the Miller U.S. Pat. No. 3,571,814 (bead of plastic material along the strip), in the Dominick U.S Pat. No. 3,632,383 (application of a heat-solidifiable composition to the edge), and in the Weatherly et al U.S. Pat. No. 4,501,782 (bonding webs by use of ultrasonic energy). The Johnson U.S Pat. No. 4,052,095 shows a sling whose surface is protected by a lamina of an elastomeric material. The Ayase U.S. Pat. No. 4,600,626 shows an automobile seat belt whose resistance to lateral flexure is increased by the use of stiff weft yarns. The Hammersla U.S. Pat. No. 4,856,837 shows a cargo sling that is provided with protective warp yarns consisting of a vinyl sheath on a polyester core. Unfortunately, none of these prior art structures, with the possible exception of HAMMERSLA, gives adequate protection against abrasion to the edge of the strip where it is needed. The degree of resistance to cutting and abrasion is determined in those structures by the material from which the protective yarns are made. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.
It is, therefore, an outstanding object of the invention to provide a sling whose edges have extraordinary resistance to abrasion and cutting.
Another object of this invention is the provision of a sling for use in material handling, which sling has excellent strength and toughness.
A further object of the present invention is the provision of a sling which is simple and rugged in construction, which can be easily manufactured from readily obtainable materials, and which is capable of a long life of useful service with a minimum of maintenance.
A still further object of the invention is the provision of a method of treating a webbing to give it maximum abrasive resistance, particularly at the longitudinal edges of the webbing.
It is a further object of the invention to provide a synthetic fiber system to increase the resistance of an article to damage by contact with sharp edged articles.
Another object of the invention is the provision of an edge-strengthening treatment which can be easily carried out during conventional manufacturing procedures.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.